1. Field of the Invention
The present invention relates to an apparatus for steering rear wheels of a vehicle, and more particularly to an apparatus for controlling the performance of vehicle motion in steering the rear wheels of the vehicle.
2. Description of the Prior Art
In a vehicle having a rear wheel steering apparatus in addition to a conventional steering apparatus, rear wheels of the vehicle are steered as well as front wheels. The controllability and stability of the vehicle during its turning behavior are remarkably improved by properly controlling the steering angle of the rear road wheels in response to the steering angle of the front road wheels.
FIG. 8 shows a rear wheel steering apparatus previously known in the art, wherein a steering angle sensor detects a turning angle of a steering wheel 2 to determine a steering angle of front wheels FR and FL, and a vehicle speed sensor 3 detects a speed of the vehicle. Further, a stroke sensor 4 detects a direction of the rear wheels. An electronic control unit 5 operates a desired steering angle on the basis of information received from the steering angle sensor 1 and the vehicle speed sensor 3. The electronic control unit 5 monitors outputs of the stroke sensor 4 to drive a rear wheel driving apparatus 6 such that the angle of direction of the rear wheels RR and RL is made equal to the desired steering angle obtained in the electronic control unit 5.
Such a prior apparatus has been disclosed in Japanese Patent Laid-open Publication No. 62-15172, for example. In the prior apparatus, however, the desired steering angle of the rear wheels might be somewhat inaccurate if any abnormality occurs in the stroke sensor, for example. The performance of vehicle motion is hardly changed so long as the vehicle is traveling at low speed, even if the steering angle of the rear wheels becomes somewhat inaccurate. However, in the case where the vehicle is traveling at high speed, the performance of vehicle motion can be largely changed in the prior apparatus.